A=[1 -2 -3 ;3 -3 -3; -4 7 10];
A(2,:)=A(2,:)-A(2,1)/A(1,1)*A(1,:);
A(3,:)=A(3,:)-A(3,1)/A(1,1)*A(1,:);
A(3,:)=A(3,:)-A(3,2)/A(2,2)*A(2,:);
A
